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Subpanel vs Service Upgrade in Ontario (2026): A Subpanel Adds Spaces, Not Capacity; When Each One Is the Right Fix and What It Costs
Electrical & Lighting
Subpanel or Service Upgrade: More Spaces Is Not More Power
A subpanel is a power bar, not a bigger wire from the street. It gives you more places to put breakers, closer to where the work is. It does not add one amp to what the house can draw. If the panel is full, a subpanel may be the whole answer. If the house is short of power, only the service or a load manager fixes it. The load calculation tells you which problem you have.
The numbers
$1,500subpanel, attached garage or basement
$3,500subpanel, detached garage or shop with a trench
$3,800100 A to 200 A service, overhead
0 Acapacity a subpanel adds to the service
| Fix | What it solves | Range | Budget |
|---|---|---|---|
| Subpanel, attached garage or basement | Out of spaces; work far from the main panel | $600 to $2,500 | $1,500 |
| Subpanel, detached garage or shop, trenched | Power to an outbuilding | $2,500 to $4,500 and up | $3,500 |
| Garage or outbuilding subpanel at new-build rough-in | Same, planned before the walls close | $1,500 to $3,500 | $2,500 |
| Panel replacement, same amperage | Old, failing or full box with no room beside it | $1,500 to $3,000 | $2,200 |
| EV energy management system | One big load (a charger) on a tight service | $750 to $1,500 | $1,000 |
| 100 A to 200 A service, overhead | Not enough capacity | $2,500 to $5,000 | $3,800 |
| 100 A to 200 A service, underground with a trench | Not enough capacity, buried service | $5,000 to $7,000 and up | $6,000 |
October 2026, before HST. The new-build budget is the middle of its range. A subpanel price usually means the panel, its feeder and the connection; ask whether any circuits from it are included, because most published prices do not say.
Why Ontario prices are all over the map: the contractors and price guides we checked for this page quoted subpanels from one end of the province to the other. A Toronto contractor said a garage subpanel “starts at $600”, ESA extra. A national home-services marketplace said $800 to $2,500. An Eastern Ontario contractor priced a garage or outbuilding subpanel at $1,500 to $3,500 on a new build, and an Ottawa contractor guide said $2,500 to $4,500 and up for a detached garage. The difference is the feeder length, whether there is a trench, the size of the subpanel and whether the circuits are included. Budget $1,500 attached and $3,500 detached, and get two or three quotes on the same written scope.
Spaces and Capacity Are Two Different Problems
Spaces are the slots in the panel. When they run out, there is nowhere to put a new breaker. Capacity is what the service can carry, set by the main breaker and the cable from the utility, and checked by the load calculation in Rule 8-200 of the Ontario Electrical Safety Code, 2024 edition.
A subpanel is fed from a breaker in the main panel. Whatever it feeds still comes through the main breaker. Hang a 60 A subpanel off a 100 A service and you have a 100 A house with more breakers, not a 160 A house. Homeowners who believe otherwise usually find out from the main breaker.
A full panel tells you nothing about capacity on its own. A house can have every slot used and a calculated load well under 100 A, because many of its circuits feed only a few lights each. Another can have empty slots and no capacity left, because someone added a hot tub and a charger. Count both before you buy anything.
When a Subpanel Is the Right Answer
- The garage or shop. A subpanel in an attached garage keeps a dozen long runs from crossing the house. A detached garage gets a feeder in a trench to a subpanel there; the detached garage cost page prices the building around it.
- A basement finish. A new basement can add a lot of circuits: lights, receptacles, a bathroom and maybe a bar fridge. A subpanel near the work keeps the runs short and the main panel tidy.
- A basement apartment. A secondary suite often gets its own subpanel so the tenant can reach their own breakers without coming upstairs; ask the electrician what the code and ESA want for your suite. The suite rules themselves are on the basement apartment page.
- An addition at the far end of the house. Long runs cost copper and voltage. A subpanel at the addition is often cheaper than ten home runs.
In every one of those, the question is still whether the new load fits the service. A basement finish with lights and receptacles usually does. A shop with a welder, a heater and a compressor may not. The feeder to the subpanel is sized for what it serves, and its loads go into the house calculation like any other.
When Only More Capacity Fixes It
If the calculation for the house plus the new loads comes out above the service rating, no subpanel helps. ESA’s own worked example in Bulletin 8-3-15 is a 140 m2 house with air conditioning, a 12 kW range, a dryer, a storage water heater and a 32 A Level 2 charger counted at 7,680 W. It came to 26,055 W, which is 108.6 A, and needs at least a 125 A service. On paper, that ordinary house with one charger has outgrown 100 A.
There are three ways out of that:
- An energy management system on the charger, $750 to $1,500. Under Rule 8-106 the charger is then counted at what the system allows, not its full rating. This is a common fix when the only new load is one EV; the EV charger on 100 amps page covers it.
- A smaller load. A charger set to a lower current, or a heat pump with smaller backup heat, can bring the number under the line.
- A service upgrade, $3,800 overhead or $6,000 underground. This is the answer when several big loads are coming: heat pump with electric backup, charger, hot tub. The panel upgrade cost page prices it.
Rule 8-106 also lets an existing service be evaluated with measured actual demand when load is added. That is a call only a licensed electrical contractor and ESA make, with real data, not a guess from the basement stairs.
Tandem Breakers and the Panel That Is Out of Room
Tandem breakers put two circuits in one space. Some panels accept them in some positions, some accept none, and the panel label says which and what type. Your electrician reads the label; if the label says no, the answer is no, however much room it would save.
Tandems are a reasonable way to add one or two circuits to a panel that allows them. They are not a plan for a basement finish. A panel that has been tandemed to the last slot is usually a panel that should have had a subpanel beside it ten years ago. And remember that most new receptacle circuits in a house need arc-fault protection, which takes the breaker type out of your hands.
- Run the load calculation first. It decides between subpanel, load manager and upgrade.
- Out of spaces, plenty of capacity: subpanel.
- One big new load, tight capacity: load manager or a smaller load.
- Several big new loads: service upgrade, and add a subpanel at the same time if you need spaces too.
- Every option: an ESA notification filed before work starts, and an ESA Licensed Electrical Contractor if you hire anyone. A handyman is not licensed to do it.
Questions people ask
Does a subpanel increase my amperage?
No. It adds breaker spaces. Everything on it still comes through the main breaker and the service. Only a bigger service, or managing the loads, changes what the house can draw.
Can I put a 100 A subpanel on a 100 A service?
The subpanel can be rated higher than its feeder breaker; what matters is the feeder breaker size and the house load calculation. The house still has 100 A in total. Your electrician sizes the feeder for what the subpanel serves.
What does a garage subpanel cost in Ontario?
About $1,500 for an attached garage, in a range of $600 to $2,500, and about $3,500 for a detached garage or shop with a trench, from $2,500 to $4,500 and up. Before HST, October 2026, circuits extra.
My panel is full. Do I need 200 A?
Not necessarily. A full panel is out of spaces, which a subpanel or a few tandem breakers can solve if the panel allows them. Whether the house needs 200 A depends on the calculated load, not the number of empty slots.
Does a subpanel need a permit?
Yes. It needs an ESA notification filed before the work starts, by the licensed electrical contractor doing it, or by a homeowner doing work in their own home, who must then pass the inspection.
Spaces or capacity? Find out in five minutes
The service capacity calculator does the Rule 8-200 arithmetic for your house and the loads you plan to add, and shows whether a subpanel, a load manager or an upgrade is the fix. If you already have a quote for one of them, the $99 review reads it, or up to three, and checks it against the numbers.
Sources and further reading
- ESA Bulletin 8-3-15: demand factors: ESA’s worked load calculation for a house with air conditioning, a range and a Level 2 charger.
- ESA Bulletin 86-1-7: electric vehicle charging systems: how an EV charger is counted in the load calculation and how an energy management system changes it.
- ESA notifications and inspections: when a notification of work is needed, who files it, and the rule that nothing is covered until an inspector authorizes it.
